1. Field of the Invention
This invention relates generally to gas turbine electrical power generation and more specifically to a rankine-microturbine as a combined cycle turbine system having a common rotor shaft, incorporating a steam turbine with a gas turbine rotor spool with an integral alternator rotor in close proximity and co-axially within a laminated iron stator with wires to generate electricity.
2. Description of Prior Art
It can be appreciated that microturbines, a non-synchronous electrical power generator, have been in use for years. Typically, microturbines are comprised of gas turbines such as in U.S. Pat. Nos. 6,314,717, 6,605,928, 5,497,615 and Japanese patent 061737714 and currently demonstrate <30% cycle efficiency incorporating heat exchangers, <15% cycle efficiency without heat exchangers and the hybrid-microturbine of application Ser. No. 10/809,719 having <23% cycle efficiency incorporates a staged compressor for improved cycle efficiency without a heat exchanger. All the above can be incorporated into Combined Heat and Power (CHP) system to attain higher thermal efficiency. Synchronous electrical power generation typical of current electrical power-plants include the simple turbojet, a single spool type gas turbine with electrical output power efficiency approaching 43%, a combined cycle turbine system having a gas turbine driving a generator and separate steam turbine extracting heat energy from the gas turbine exhaust to drive another generator and combining the electrical output power to yield efficiency near 60%. More recently, large combined cycle turbines have been introduced as in GE patent 6897577 where the gas turbine and steam turbine are clutch coupled to drive a common generator and expected to yield >60% electrical output power efficiency. Other gas turbine companies offering a similar clutch coupled synchronous driven common generator idea include Siemens (Diesel & Gas Turbine World of Feb. 2006 article) and Westinghouse (ASME PWR2004-52072 proceeding). Microturbines (non synchronous generators), typically less than 500 Kw offer some advantages either in line tie or island system especially in a CHP cycle but still lack high electrical output power efficiencies for opportunities in main power applications. Combined cycle electrical power systems have synchronous power generators and are large power-plants and have either separate generators for the steam and gas turbines or more recently use a clutch coupled steam turbine and gas turbine to drive a common generator yielding >60% electrical output power efficiency; but are too complex and expensive for smaller power-plant applications. Complexity will lend to higher power plant maintenance cost even thou the fuel cost is the biggest factor in the $/Kw-hr billing. Another issue with conventional microturbines is the use of heat exchanger to attain ˜30 efficiency is still too low for distributed continuous main power applications and with the heat exchanger there are limitations on start-up and shut-down cycles concerning turbine exhaust gas temperature as high as 1300F and material costs life cycle considerations.
A hybridmicroturbine with its staged higher compressor ratio (˜23% at maximum power) has higher efficiency at off design than that of the microturbine with heat exchanger and does not have start up or shut down limitation like this microturbine; but due to the lower efficiency, has limited main grid power uses. The microturbine and hybrid microturbine with low emissions, multifuel capability and minimal maintenance will greatly replace the reciprocating generator sets (gensets) with $/Kw initial purchase cost being competitive; the latter is most evident in the hybrid microturbine along with portability offering low weight (no exhaust gas heat exchanger).
While these devices may be suitable for the particular purpose to which they address, they are not as suitable for providing a combined cycle turbine system with a common shaft between the steam turbine and the gas turbine integral alternator rotor as a one spool rotor system to yield high electrical power cycle efficiency, simplicity, reduced installation cost and maintenance. This smaller main power-plant would lend itself to stand alone communities, business, and industrial applications or simply more available to distributed energy without major disruptive events either man made or weather related. Low emissions is a major feature and lower fuel use means lower CO2. In these respects, the Rankine-Microturbine according to the present invention substantially departs from the conventional concepts and design of the prior art, and in so doing provides an apparatus primarily developed for the purpose of providing a combined cycle turbine system with a common shaft between the steam turbine and the gas turbine integral alternator rotor as a one spool rotor system to yield high output electrical power efficiency, simplicity, reduced installation cost and low fuel use.